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C4 – C in 4 functions

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Re: C4 – C in 4 functions

#11

Post by mturmon »

marcofiset wrote: post #4

I honestly think this is ridiculous. Sure, this is an incredible feat, and congrats. But serioulsy, I would be ashamed to publish such unreadable code under my name. What about naming your variables with descriptive names? What about extracting complex conditions into well named function to understand what is going on (thus defeating the purpose of the "4 functions") ? This list could go on forever... Writing softwar…

> This list could go on forever...

Yes it could. While you are adding to your list of coding rules, the OP will have written another fun, tiny compiler.

Who is having more fun?

Re: C4 – C in 4 functions

#12

Post by cbhl »

TazeTSchnitzel wrote: post #8

Pretty damn impressive. Though I must wonder: how complete is it? What does it and does it not support? It's at least complete enough to be self-hosting, but beyond that? The code doesn't use that much of C.

Judging from the comments in c4.cpp, it probably only supports enough of a subset to compile itself.

Granted, while building a parser that can parse (let alone compiling) the full C language is nontrivial, any undergrad should be able to build a parser and compiler for a sufficiently simple subset of it. (In my undergrad, we used this subset to build a "compiler" in second year: https://www.student.cs.uwaterloo.ca/~cs241/wlp4/WLP4.html)

Re: C4 – C in 4 functions

#13

Post by JoeAltmaier »

cbhl wrote: post #12
TazeTSchnitzel wrote: post #8

Pretty damn impressive. Though I must wonder: how complete is it? What does it and does it not support? It's at least complete enough to be self-hosting, but beyond that? The code doesn't use that much of C.

Judging from the comments in c4.cpp, it probably only supports enough of a subset to compile itself. Granted, while building a parser that can parse (let alone compiling) the full C language is nontrivial, any undergrad should be able to build a parser and compiler for a sufficiently simple subset of it. (In my undergrad, we used this subset to build a "compiler" in second year: https://www.student.cs.uwaterloo.ca/~c…

You can build a C parser in an afternoon. It only has a few language constructs. Declarations are the hardest. Scanners are readily available for expressions and constants.

Re: C4 – C in 4 functions

#14

Post by Lerc »

TazeTSchnitzel wrote: post #8

Pretty damn impressive. Though I must wonder: how complete is it? What does it and does it not support? It's at least complete enough to be self-hosting, but beyond that? The code doesn't use that much of C.

It's clear from the huge number of 'else if' statements that it doesn't support switch statements.

This is also a bit of a clue

    p = "char else enum if int return while "
    "open read close printf malloc memset memcmp exit main";

Re: C4 – C in 4 functions

#15

Post by cbhl »

marcofiset wrote: post #4

I honestly think this is ridiculous. Sure, this is an incredible feat, and congrats. But serioulsy, I would be ashamed to publish such unreadable code under my name. What about naming your variables with descriptive names? What about extracting complex conditions into well named function to understand what is going on (thus defeating the purpose of the "4 functions") ? This list could go on forever... Writing softwar…

I actually found the code surprisingly easy to read; "tk" stands for "token", "ty" for "type", and so forth.

It's worth noting that compilers don't pop out of thin air -- you have to start with something simple in order to compile a more complicated compiler. Bootstrapping your own self-hosting compiler is a useful academic exercise, and you should try it sometime if you haven't already: http://en.wikipedia.org/wiki/Bootstrapping_(compilers)

Re: C4 – C in 4 functions

#17

Post by cbhl »

JoeAltmaier wrote: post #13
cbhl wrote: post #12

Earlier quoted context omitted.

Judging from the comments in c4.cpp, it probably only supports enough of a subset to compile itself. Granted, while building a parser that can parse (let alone compiling) the full C language is nontrivial, any undergrad should be able to build a parser and compiler for a sufficiently simple subset of it. (In my undergrad, we used this subset to build a "compiler" in second year: https://www.student.cs.uwaterloo.ca/~c…

You can build a C parser in an afternoon. It only has a few language constructs. Declarations are the hardest. Scanners are readily available for expressions and constants.

I would be worried about handling the not-context-free parts of the language: http://trevorjim.com/c-and-cplusplus-are-not-context-free/

How would you handle these?

Re: C4 – C in 4 functions

#19

Post by TazeTSchnitzel »

Lerc wrote: post #14
TazeTSchnitzel wrote: post #8

Pretty damn impressive. Though I must wonder: how complete is it? What does it and does it not support? It's at least complete enough to be self-hosting, but beyond that? The code doesn't use that much of C.

It's clear from the huge number of 'else if' statements that it doesn't support switch statements. This is also a bit of a clue p = "char else enum if int return while " "open read close printf malloc memset memcmp exit main";

Ah, the lack of struct explains why the compiler doesn't use any structs.

Re: C4 – C in 4 functions

#20

Post by JoeAltmaier »

cbhl wrote: post #17
JoeAltmaier wrote: post #13

Earlier quoted context omitted.

You can build a C parser in an afternoon. It only has a few language constructs. Declarations are the hardest. Scanners are readily available for expressions and constants.

I would be worried about handling the not-context-free parts of the language: http://trevorjim.com/c-and-cplusplus-are-not-context-free/ How would you handle these?

Scanner has to have access to the symbol table, emit 'ident' or 'type' as appropriate. So not a pure context-free parser.
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